Air heating gas burner



April 13, 1965 R. H. YEO ETAL AIR HEATING GAS BURNER 2 Sheets-Sheet 1 INVENTORS Robe/f H. Yeo Oar/D. Wall/500m. M 44/41 fmj Filed March 5, 1963 A ril 13, 1965 H. YEO ETAL 3,178,161

AIR HEATING GAS BURNER Filed March 5, 1965 2 Sheets-Sheet 2 ("Q I 'l O INVENTORS Robe/f h. 760 BY Car/D. Wa/r/sfrom 7071, 44/11414 jaw;

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United States Patent I 3,173,161 AIR HEATING GAS BURNER Robert H. Yeo and jar DavidWahlstrorn, Muncie, Ind, assignors to Maxon Premix Burner Company, Inc., Muncie, Ind, a corporation of Indiana Filed Mar. 5, 1963, Ser. No. 262,883 14 Claims. (Cl. 263-19) The present invention relates to gas burner systems and, more specifically, to gas burners adapted to be disposed in and to heat an air stream.

It is an object of the present invention to provide a gas burner which is especially adapted for operation in and for heating an air stream that supplies all or a substantial percentage of the oxygen required to assure complete combustion, the amount of oxygen used depending upon whether the burner fuel comprises raw gas or a gas air mixture. p

It is another object of-"the present invention to provide an air heating gas burner that has a wide turn-do'wnratio, i.e., a high ratio between its" maximum and minimum firing rates, and further that can be readily throttled or adjusted over its entire operatingrange' with a smooth and continuous-variation in its heating output.

It is a further object of the present invention to provide an air-heating'gas burner that'isspecifically an improvement' over the type of gas burner disclosed in theYeo et al. Patent No. 3,051,464;

It is yet a further object of theprese'nt invention to provide a new and improved gas burner that is adapted to operate in andheat an air stream by utilizing a small amount of the air stream to effect at all firing rates, i.e. low, intermediate and-high, complete stoichiometric combustion of the burner fuel whether raw gas or gas-air mixtures.

It is still another object of the present invention to provide an air stream burner having improved flame retention properties and-high quality combustion-characteristics when raw gas is used as the burner fuel.

It is another object of the present invention'to'provide an air stream gas burner'that is constructed so-as-toprotect the combustion process at low firing ratesfrom the negative pressure created within the gas burner by the air stream.

It is yet another object of the present invention 1101011 vide a gas burner that is especially adapted for operation in'and for heating an air stream by using' a portion of the air stream at low firing rates to achieve a better performance at low firing rates than comparable prior art burners.

It is still a further object of the present invention to provide an airstream'gas burner that embodies improved flame retention properties;

It is another object in accordance with the previous object to provide a burner that has flame protectivecharacteristics particularly at low firing rates. I

It is another object of the present invention in acco'rd ance with any of the previous objects to provide a gas burner that is easily and'inexpensively manufactured and, in addition, that requires reduced maintenance expense.

The above and other objects are achieved in accord ance with the present invention'by providing a gas burner system adapted to heat an air stream moving at a desired velocity. More specifically, the air stream system embodies a gas burner adapted to be disposed within and'to 3,178,3hi Patented Apr. 13, 1965 heat an air stream by utilizing a portion' of the air stream to effect complete combustion of the burner fuel, i.e., either raw gas or gas-air mixtures; The burner is'so constructed that it has a high or wide turn-down ratio, i.e., a high ratio between its maximum and minimum firing rates, and further, it can be readily throttledover its entire range of operation with a smooth and continuous variation of its heat output. More specifically, the gas burner embodies a burner casting and a mixing plate means supported from the casting. In one aspect of theinvention the burner is so constructed that combustion of the burner fuel at low firing rates is protected from the negative pressure created within the burner by the air stream. In another aspect of the invention, the same construction offe'rs-fiame retention properties, for example, at intermediate and high'firing rates, and is continuously cooled by' the air stream, thereby eliminating either deterioration and/or replacement of the construction. Thus, a gas burner of the type embodying the features of the present invention does not embody ignitionrails, flame retention bars, flame targets, or the like and, accordinglyfthe initial cost of these components and their subsequent maintenance is eliminated.

The invention, both as to its'organization and method of operation, taken with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 isa diagrammatic view of a" gas bu'rner system including a gas burner embodying the features of the present invention, the gas burner system being illustrated as used with raw gas fuel; 7

FIG. 2 is an enlarged fragmetna'ry perspective view of one embodiment of the gas burner of FIG. 1;

FIG; 3 is a sectional view taken along line 33 of FIG. 2;

FIG. 4 is an enlargedfra'gmentary view of FIG. 3

FIG. 5 is a sectional view, somewhat smaller in size than FIG. 3, of another embodiment of the gas burner of FIG. 1; v

FIG; 6 is a'sectional view, similar in size to FIG. 5, of yet another embodimentof the gas burner of PEG. 1;

FIG. 7 is a sectional view, similar in size to FIG. 3, of still another embodiment of the gas burner of FIG. 1;

FIG. 8 is a sectional view, similar insize to FIG. 3, of a further embodiment of the gas burner of FIG. 1; and

FIG. 9 is a diagrammatic view ofanother form of the gas burner system of FIG; 1; thegas'bu'rner' system" being illustrated as used with a gas-air mixture from a premixer arrangement.

Referring now to the drawings, there are illustrated burner systems embodying air stream gas burners adapted to be supplied WlihClilll' type of burner fuel, i.e., either raw gas or agas-air mixture. More specifically, there is illustrated in FIG. 1' a burner system ll) of the type adapted to'be used with raw gas, while there is'illustrated in'F IG. 9 a burner system of the type adapted to be used witha gas-air mixture. Without in any way'limiting the scope of usage of the system 100, it has particular utility in (1) heating make-up'air for factories and other manufacturing and processing establishments, supplying heated air for ventilating and other processes and/ or supplementing the normal space heating facilities, (2) heating air for industrial ovens and similar facilities in which recirculating hot-air-in-motion is used as a processing medium for drying, baking, curing, tempering, and other similar industrial and commercial processes, and (3) heating air in simple non-recirculating drying applications. Without in any Way limiting the scope of usage of the system 10, it has particular utility in the above identified installations Nos. 1 and 3. If the system is used with the above identified installation No. 2, auxiliary air or oxygen necessarily has to be supplied to the system, because in a closed recirculating system all of the oxygen would in a relatively short time be consumed in the combustion process.

The systems 10 and 100, as illustrated in FIGS. 1 and 9 respectively, are generally similar in construction, with the exception that the system 100 embodies a premixer arrangement 110 for producing the desired gas-air mixture. In all other respects, the systems are identical. More specifically, the system 10 includes an air stream 12 conveyed through a duct 14 past a gas burner 16 under the control of a blower 18. The air stream 12 may be either a fresh air stream, for example, wherein the duct 14 is connected to a fresh air inlet grill 20, or the air stream may be a recirculating stream, for example, wherein the duct 14 is part of a recirculating duct arrangement of an industrial oven or the like and sufiicient fresh air or oxygen to permit complete combustion is added to the recirculating stream at a point not shown. In either event, the velocity of the air stream in the duct is determined by the type and size of the blower 18 and/ or by profile plates extending between the burner and the duct 14. Thus, in accordance with the demands and requirements of the particular installation, the air stream velocity is set at a particular value within the range of approximately 1,500 to approximately 4,000 feet per minute. It should be understood, of course, that the blower 18 may be located either on the upstream or downstream side of the burner 16.

As set forth in the above referred to Yeo et al. Patent No. 3,051,464, the gas burner 16 is made up of burner elements or units forming a desired pattern across the area of the duct. The heating flame occurs in a substantially continuous line or band along the length of each burner unit and the burner shown distributes the flame and heat in a desired pattern across the air stream 12. The gas burner 16. is supported by means (not shown) centrally within the duct 14 in transverse relationship to the moving air stream, whereby the air stream is substantially uniformly heated by the burner 16. As illustrated in FIG. 1, the burner 16 is connected to a supply line 22 which, in turn, is connected to a raw gas line 24. The pressure and/or velocity of the raw gas supplied to the burner 16 is varied and controlled by any suitable means (not shown), for example, by a valve or the like, to effect a Wide range of firing rates, e.g., low, intermediate, and high firing rates.

Similar to the system 10 of FIG. 1, in the system 100 an air stream 112 flows through a duct 114 past a gas burner 116 under the control of a blower 118. For all practical purposes, the air streams 12 and 112, the ducts 14 and 114, the burners 16 and 116, and the blowers 18 and 118 are respectively identical in construction. However, in contrast to the system 10, the system 100 embodies a gas-air premixer arrangement 110 which is suitably connected to the gas burner 116 by a supply line 122. It should be appreciated that premixing arrangements, other than that illustrated and described hereinafter, may also be used. The illustrated premixer arrangement 11%) has a gas inlet pipe 124 and an air inlet shutter 126 and is adapted not only to supply regulated amounts of gas-air mixture, but also to control the proportions of gas and air in the mixture and to provide different proportions in the mixture at different rates of mixture supply.

Considering now the gas burner, per se, embracing the features of the present invention, one embodiment of the gas burner is illustrated in FIGS. 2, 3, and 4 and is identified by reference numeral 16, another embodiment of the gas burner is illustrated in FIG. 5 and is identified by reference numeral 216, yet another embodiment of the gas burner is illustrated in FIG. 6, and is identified by reference numeral 316, still another embodiment of the gas burner is illustrated in FIG. 7 and is identified by reference numeral 416, and a further embodiment of the gas burner is illustrated in FIG. 8 and is identified by reference numeral 516. Contrary to the prior art burners, each of the gas burners 16, 216, 316, 416 and 516 cmbodies means that perform the dual function of effecting flame retention at intermediate and high firing rates and, also, protecting combustion at low firing rates. The flame retention and protective means are continuously bathed throughout substantially the entire extent of their dimensions by the air stream and are thereby continuously cooled by the air stream with the result that overheating or the like is avoided. As a result, ignition rails, flame retention bars, flame targets and the like are eliminated with the attendant savings in fabrication, installation, and maintenance. As previously suggested, each of the embodiments 16, 216, 316, 416 and 516 is adapted to be used in either of the systems 10 and 100, and, consequently, each is adapted to be used with either kind of burner fuel, i.e., raw gas or gas-air mixture.

Without indicating an order of preference, the gas burner 16 illustrated in FIGS. 2, 3, and 4 will be first described. Briefly, the gas burner 16 comprises an elongated burner casting 30 that manifolds the burner fuel to spaced apart ports 42 through which issues the burner fuel. Supported from the casting 30 is a pair of generally diverging protective and mixing plates 32, 34 that effect complete combustion at all firing rates between low and high firing rates, in a manner taught by the above Yeo et a1. Patent No. 3,051,464. The burner 16 is disposed within the air stream so that the casting 30 (the rear of the burner 16) is upstream of the protective and mixing plates 32, 34 (the front of the burner 16). As illus trated, the casting 30 faces upstream in opposition to the direction of flow of the air stream, and the plates 32, 34 face or open downstream in the direction of flow of the air stream. As a result, the casting 30 divides the air stream and directs it along the casting (to the right as viewed in FIG. 1) onto the upstream surface of the protective and mixing plates 32, 34. The plates 32, 34 are suitably apertured so that a part of the air stream passes, in the form of inwardly and forwardly directed jets of air, into a protective mixing space 35 and also into a general mixing space 37defined between the mixing plates 32, 34. By this arrangement, the burner fuel issuing from the casing ports 42 is intimately mixed with the jets of air to effect a highly controlled and complete com bustion of the burner fuel throughout the entire firing range of the burner 16.

Referring now more specifically to the constructional details of the gas burner 16, attention is invited particularly to the burner casting 30, best illustrated in FIGS. 2 and 3. As shown, the casting comprises a manifold section 36 forming a fuel conduit having at its opposite ends attachment flanges 38. The manifold section 36 is generally tear-shaped in cross section and has formed on its downstream side a fiat wall 40. The burner ports 42 are disposed in a row longitudinally along the center of the wall 40 so as to communicate with the fuel conduit or manifold section 36. The upstream side, comprising a generally hemicylindrical section 44, presents a streamlined contour to the air stream and is connected to the flat wall 40 by a pair of converging, generally fiat wall sections 46 and 48. As a result, the air stream engages the generally cylindrical upstream section 44,-

passes around the section 44, flows forwardly along the converging sections 46 and 48, and passes onto and along the protective and mixing plates 32 and 34.

v As clearly shown in FIGS. 2 and 3, the protective and mixing plates 32 and 34 are each generally angulated and each includes a flange 50 and 52 respectively secured to the converging wall sections 46 and 43. Extending forwardly of and in the planes of the flanges 5t} and 52 are protective sections 54 and 56 oriented to converge forwardly and inwardly from the casting 3% to define the progressively smaller, protective mixing space 35. Angularly related to the protective sections are mixing sections 58 and 60 that diverge forwardly and outwardly relative to the burner casting 30 to define a trough or progressively larger, general mixing space 37. As shown, each of the protective sections 54 and 56 is provided with a single row of relatively small, spaced-apart apertures 62 and 64, respectively, while the mixing sections 58 and 60 each includes a plurality of rows of spaced apart apertures. As best seen in FIG. 2, the mixing section 58 in cludes a bottom row of relatively small apertures 66, a second row of intermediate sized apertures 68, a third and fourth row of larger apertures 79 and 72. The mixing section 60 includes similarly located rows of correspondingly similar apertures 74, 76, 78, and 86. It will be appreciated that the apertures can assume different configurations, but in the form shown, the apertures are circular and are simply stamped out of the plates 32 and 34.

By the use of the above apertured construction, as the air stream moves forwardly over the shielding and mixing plates 32 and 34, portions of the air stream pass into the openings 62, 64, 65, 68, 70, 72, 74, 76, 78, and 8%. As a result, air jets issue through these apertures for intimate mixture with the burner fuel issuing from the burner ports 42, with the result that, irrespective of the velocity of the burner fuel issuing through the ports 42, controlled and complete combustion occurs substantially between the plates 32, 34. More specifically, the air jets passing through the apertures 62 and 64 of the protective sections 54 and 56 effect complete combustion of the burner fuel at the low firing rates, whereas the air jets passing through the apertures 6674, 68-76, Yd-7S, and 72-88 progressively assure complete combustion of the burner fuel at firing rates progressively higher than low firing rates, for example, intermediate firing rates and high firing rates. The action of the burner fuel and air jets passing through the mixing sections 58 and 60 is clearly described in the above-identified Yeo et al. patent and, in the interest of avoiding unnecessary duplication, such action is not described.

The action of the burner fuel and air jets passing through the apertures 62 and 64 in the protective sections 54 and 56 is generally similar to the above described action. Of course, at low firing rates only the air jets passing through apertures 62 and 64 are involved in the cornbustion of the raw gas fuel. Inasmuch as the apertures 62 and 64 are oriented rearwardly inwardly, the air is drawn into the apertures at a relatively low velocityas a result of the vacuum created in the general mixing space 37 by the air stream passing over the plates 32 and 34.

In many installations, the gas burner 16 is disposed in a fast moving air stream having a particular velocity within the range of approximately 1500 to approximately 4000 feet per minute. With the gas burner oriented as described above, i,e., with the burner casting 3t} upstream of the plates 32 and 34, the air stream flowing past the plates 32 and 34 creates between the plates a reduced pressure or vacuum that tends to increase the speed of the burner fuel. In burners designed without the novel features of the new invention, such a vacuum plus the impact of the air jets will create performance dificulties at low firing rates. For exainple, stable cross ignition from one portion of the burner to the other is impaired at low firing rates, or, portions of the flame may go out entirely unless relatively high minimum firing rates are maintained. As a result, the turn-down range of the burner is reduced substantially. In certain prior art devices, rails, flame retention bars, flame targets, or similar auxiliary constructions have been used to restrict or slow down the speed of the burner fuel, thereby to improve cross-ignition and/ or flame retention. Such ignition rails, flame retention bars, flame targets, and the like add to the manufacturing cost of the burner and, in addition, are generally exposed directly to the flame. Accordingly, these .components are exposed to rapid deterioration with the attendant maintenance problem.

In contrast to the prior art burners and in accordance with an aspect of the present invention, combined flame protection and flame retention means are embodied in the plates 32 and 34. To this end, the shielding and mixing plates 32 and 34 are configured so that the forward portions of the protective sections 54 and 56 and the rearward portions of the mixing sections 58 and 60 define a necked, restricted, or throated structure. Although the protective sections 54 and 56 are apertured as indicated at 62 and 64, the necked construction (and specifically the protective sections 54 and 56) performs a flame protective function in that it at least partially isolates and protects the mixing space 35 from the negative pressure developed by the air stream. Hence, complete combustion can be achieved at exceptionally low firing rates, with the result that the burner 16 has a relatively high turndown ratio.

It will be appreciated that, in addition, the necked construction assures that a continuous and smooth transition is obtained throughout the entire range of burner operation, i.e., from low firing rates to high firing rates. Expressed in another way, the heat developed by the burner 16 is gradually and/ or substantially linearly changed, in contrast to being stepped or increment-ally changed. This result is possible because the necked construction (and specifically the protective sections 54 and 56) provides a desired negative pressure within the mixing space 35 throughout its entire range of operation. Actually, the protective sections 54 and 56 on the upstream side of the neck act on the fuel issuing from the burner ports 42 so as to cause the negative pressure developed by the air stream to be relieved. As a result, part of the fuel from the ports 42 and the air jets issuing from the apertures 62 and 64- are permitted to mix thereby to produce and to maintain combustion in the protective space 35. Consequently, irrespective of the firing rate of the burner 16, flame is present in the mixing space 35 so that as the firing rate increases from its low rate, theflame extends forwardly through the throat 35 and onto the mixing plates 58 and 69.

In a burner embodying a V-shaped construction, instead of a necked construction, as the firing rate is increased from its low firing rate, the velocity of flow of fuel from the burner ports 42 increases, with the result that the flame is displaced from the protective mixing space and advances forwardly onto the mixing plates 58 and 69. Consequently, the transition from low firing to intermediate firing is not smooth and continuous but, conversely, the firing rate abruptly changes and a discontinuity of heat generation occurs. In addition, the transition of flame is unattractive and appears to be unstable. In short, by using the necked construction, flame is maintained adjacent to the end wall or face 40 and smooth and continuous heat generation is provided, particularly between the low and intermediate firing rates of the burner 16.

In accordance with another aspect of the present invention, the necked construction (and specifically the mixing sections 58 and 69) performs a flame retentive function at intermediate and high firing rates, i.e., it effectively prevents bloW-out of the flame at these firing rates. As clearly shown in FIG. 4, the necked construction defines a restricted throat 82 through which raw gas 'and/ or flame pass. Actually, the rearward portions of the mixing sections 58 and 6!) on the downstream side of the neck cause eddy currents, identified by arrowed lines 83, to be developed on the downstream side of the throat 82 incident to passage of the gas and/ or flame through the throat 82. Consequently, there is produced vacuum pockets or the like that effectively trap and maintain spaced apart ribbons of flame immediately downstream of the throat 82. Hence, at intermediate and exceptionally high firing rates, combustion of the high velocity raw gas is maintained and flame blow-out is prevented.

In accordance with still another aspect of the present invention, the necked construction is continuously cooled by the air stream flowing forwardly from the burner casting 30 onto and over the plates 32 and 34. As clearly shown in FIG. 3, the air stream washes the upstream part of the necked construction, i.e., the protective sections 54 and 56, and washes the downstream part of the necked construction, i.e., the mixing sections 58 and 60. Because the plates 32 and 34 are made from a material having high heat transfer properties, any heating of the throat area 82 is rapidly dissipated in a direction toward the rear of the burner 16 by the sections 54 and 56 and in a direction toward the front of the burner 16 by the sections 58 and 60. With the necked construction acting to conduct the heat away from the throat area 82 in both the upstream and downstream directions, overheating or undue heating of the area is entirely obviated. Hence, in contrast to those gas burners that embody ignition rails, flame retention bars, etc., the necked" construction of'the present invention is not sub ject to deterioration or replacement, with the result that substantial savings in maintenance and operational costs are realized.

The gas burner 216, illustrated in FIG. 5, is structurally and functionally substantially identical to the gas burner 16. To this end, the burner 216 embodies a necked construction which performs a flame protective and flame retentive function, yet, similar to the burner 16, is continuously cooled by the air stream. However, in con trast to the gas burner 16, in which the necked construction is embodied in the plates 32 and 34-, the necked construction in burner 216 is embodied in the burner casting itself. More specifically, the burner casting 230, as shown in FIG. 5, embodies a manifold section 236 forming a gas conduit having attachment flanges 238 at its ends. The manifold section 236, similar to the manifold section 36, is generally tear-shaped in cross-section with the exception of its downstream end. Instead of the front end of the burner casting 230 having a flat end wall or face 240 (similar to end wall 40 of the burner 16), the front end embodies a necked construction comprising a pair of angulated extensions 254 and 256. The extensions 254 and 256 depend forwardly from an intermediate wall 240 in which is defined a row of burner ports 242 arranged longitudinally along its center.

More particularly, the extensions 254 and 256 actually are extensions of generally converging side walls 246 and 248 and thus initially converge inwardly and forwardly to define a progressively smaller protective mixing space 235, similar in shape and function to the mixing space 35 defined by the plates 32 and 34 in the burner 16. Apertures 262 and 264 are provided in the converging extensions to permit a portion of the air stream to pass into the protected space 235 to provide the necessary air for the raw gas fuel at low firing rates. At its throat 282, the extensions 254 and 256 diverge forwardly and outwardly, similar to the forward portions of the plates 32 and 34 in the burner 16. Suitable apertures 266 and 274 are provided in the diverging parts of the extensions to function similarly to apertures 66 and 74 in the mixing sections 58 and 66.

A pair of mixing plates 25S and 269 are respectively attached to the upstream sides of the diverging parts of the extensions 254 and 256 so as to extend rearwardly and outwardly relative to the body casing to define a genplates 253 and 266, similar to the mixing sections 58 and 69, respectively include a plurality of rows of apertures 266263-27tl-272 and 274476458486. However, in contrast to the form of the apertures 66 through 80, each of the apertures 266through 2.80 is rectangular and is simply formed by striking outward from the mixing wall tongues of metal. Such tongues are desirably left as outward projections, oriented substantially normal to the plates 2.58 and 261 to deflect air from the air stream through the apertures. The tongues associated with the apertures 266 through 280 are respectively identified as 267, 269, 271, 273, 275, 277, 279 and 281. In view of the fact that the apertures 266 through 280 have'the same relative size as the apertures 66 through 86, the tongues 267 through 281 have the same relative size.

In contrast to the burner 16, the burner 216 has flame retention properties in addition'to that of the necked construction. Specifically, because of the overlapping relationship of the casting extensions 254, 256, and the mixing plates 258 and 260, eddy or vacuum pockets are developed adjacent the forwardly facing ends of the extensions, with the result that a second pair of spacedapart ribbons of flame is produced at the forward side of the extensions 254, 256, at least at intermediate firing rates.

The gas burner 316 illustrated in FIG. 6 is similar to the gas burner 16, with the exception that its mixing sections are configured to embody flame retention means. More specifically, the gas burner 316 embodies a burner casting 33f), identically constructed to the burner casting 3t and a pair of protective and mixing plates 332 and 334, respectively, which are suitably secured to the casing walls 346 and 348 to provide a generally forwardly diverging construction, similar to the relative configuration of the plates 32 and 34 of the gas burner 16. The plates 332 and 334 embody a necked construction identical to the necked construction embodied in the plates 32 and 34 of the burner 16 and, hence, perform the same flame protective function and flame retentive function. The mixing sections 358 and 360, while oriented in the same manner as the mixing sections 58 and 66, are corrugated and are not flat as are the sections 58 and 60.

More specifically, the mixing sections 358 and 360 include generally complementary, inwardly projecting ridges located between adjacent rows of apertures 366 through 386. The ridges on the mixing section 358, proceeding in a downstream direction are identified by reference numeral 381, 382., 383, while the ridges on the mixing section 368 are identified by reference numerals 384, 385, and 386. By this construction, eddy or vacuum pockets are created on the downstream side of each of the ridges 381 through 386, so that pairs of spaced-apart ribbons of flame are trapped or produced at spaced apart lines across the downstream surfaces of the mixing sections 358 and 366. Hence, irrespective of the high firing rate of the burner 316, flame retention is maintained and complete combustion of the high velocity burner fuel is assured.

The gas burner 416, illustrated in FIG. 7, is structurally and functionally identical to the gas burner 16. To this end, the burner 416 embodies a necked construction that performs both a flame protective and flame retentive function, yet similar to the burner 16 is continuously cooled by the air stream. However, in contrast to the gas burner 16, the necked construction has a more abruptly angulated structure. Specifically, the gas burner 416 embodies a burner casting 43f constructed similarly to the burner casting 3il,.including converging casing walls from which a pair of protective and mixing plates 432 and 434 generally forwardly diverge. The burner casing 436 embodies a fiat end \Vcll or face 446 having the same width as the end Wall 40 on the casting 36.

As clearly seen in FIG. 7, the plates 432 and 434 embody a necked construction generally identical to the necked construction embodied in the plates 32 and 34 of the burner 16. In addition, the plates 432 and 434 are oriented in the same general manner as the mixing plates 32 and 34, and also perform the same flame protective function and flame retentive function. However, in contrast to the plates 32 and '34, the plates .32 and 434 embody protective sections 454 and 456, the rear portions 454b, 4561) of which are oriented perpendicularly to the face 44% and the front portions 454a, 456a of which are oriented parallel to the end face 440 to define a protective space 435 having a generally rectangular cross section (in contrast to the generally triangular section of the. protective space 35). Similarly, mixing sections 458 and 460 have rear portions 458a and 469a oriented parallel to the face 446 (the portions 454a, 458a and 456a, 4643a comprising reversed or folded flanges suitably formed by deforming the plates 432 and 434). In addition, the sections 458 and 465 have intermediate sections 4581') and 46% (comprising continuations of the front portions of protective sections 454 and 456) and forwardly diverging sections 4580 and 4690 having the same orientation and configuration as the mixing plates 58 and 60 of the burner 16 to define a mixing space 437.

In order to provide oxygen for combustion of the fuel at low firing rates, rows of openings 462 and 464 are provided in the rear portions 454b, 4561) of the protective sections 454, 456. Hence, oxygen from the air stream can readily pass into the protective space 435 to mix with the fuel issuing through port's 442 in the end wall 449. Similarly, in order to supply the fuel with oxygen from the air stream at intermediate and high firing rates, the mixing plates 458 and 466 are apertured in the same manner as either of the previously described plates in the burner 16 or 216.

In a burner constructed similar to that illustrated in FIG. 7, the width of the end wall is and the width of the throat 482 is X as compared with a width of end Wall 4% and the &1," width of the throat 35. However, notwithstanding the greater width of throat 482 in the FIG. 7 embodiment, the necked construction of the plates 432 and 434 offers a greater resistance to the passage of flame than the necked construction of the plates 32 and 34 of burner 16. Specifically, the coefficient of discharge or K factor of the abruptly angulated necked construction of the plates 432 and 434 is substantially lot er than the K factor of the necked construction of the plates 32 and 34. However, notwithstanding the difference in necked constructions, any heat developed in the throat area 435 is rapidly dissipated through the folded sections 45441-4580: and 456a46t5a to the adjacent sections 45411-453b and 456b46ib. Hence, similar to the previously described FIGS. 3, 5 and 6 embodiments, the heat is rapidly dissipated in a direction toward the rear of the burner 416 and in a direction toward the front of the burner 416.

The gas burner 516, illustrated in FIG. 8, is structurally and functionally substantially identical to the gas burner 16. To this end, the burner 216 embodies a necked construction which performs a flame protective and flame retentive function, yet similar to the burner 16 is continuously cooled by the air stream. In contrast to the gas burner 16 in which the necked construction embodies converging protective sections 54 and 56, the necked construction in the burner 516 embodies protective sections that initially forwardly diverge and then converge.

More specifically, the burner casting 53d embodies a manifold section 536 forming a gas conduit having attachment flanges 538 at its end. The manifold section 536, similar to the manifold section 36, is generally tear-shaped incross section. However, in contrast to the casting 36, the flat end wall or face 549 is substantially more narrow than the flat end wall 4%) of the burner 16; in a burner built as shown in FIG. 8, the face 545 had a width of 4". In addition, the gas burner 516 embodies a pair of protective and mixing plates 532 and 534, respectively, which are suitably secured to forwardly converging casing walls 546 and 543 to provide a generally forwardly diverging construction, similar to the general configuration of the plates 32 and 34 of the burner 16. The plates 532 and 534 embody a necked construction similar to the necked construction embodied in plates 32 and 34 of the burner 16.

As clearly seen in FIG. 8, the plates 532 and 534 embody protective sections 554 and 556 extending forwardly from the face 549 of the casting 530 and, in addition, diverging mixing plates 553 and 560. However, in contrast to the converging protective plates 54 and 56 of the burner 16, the protective plates 554 and 556 embody, respectively, sections 554a and 556a that diverge forwardly relative to the end wall 540 and, further, embody sections 5545 and 55619 that converge forwardly from the end wall or face 54% to form a protective mixing space 535. Each section 55401, 55412, 556a and 556b has the same dimensions so as to provide a pair of face-to-face troughs. As a result, the forward ends of the protective sections 554 and 556 define a throat 582 having the same width as the end wall or face 540, i.e., Similar to the plates 32 and 34, mixing sections 558 and 568 diverge forwardly from the throat 582 to define a mixing space 537. In all other respects the mixing sections 558 and 56% are identically constructed to the mixing sections of the burner 16.

In order to provide oxygen for combustion of the fuel at low firing rates, rows of openings 562 and 564 are provided in the rear sections 554a and 556a of the protective sections 554, 556. Hence, oxygen from the air stream can readily pass into the protective space 535 to mix with the fuel issuing through ports 542 on the end wall 546. Similarly, in order to supply the fuel with additional oxygen from the air stream at intermediate and high firing rates, the mixing plates 558 and 566 are apertured in the same manner as either of the previously described plates in the burners 16 or 216.

It will be appreciated that the necked construction of the plates 532 and 534 perform the identical functions as the necked construction of the burners 216, 316, and 416 previously described. It will be apparent that any heat developed in the throat area 582 is dissipated in a direction toward the rear of the burner 516 by the sections 554 and 556 and in a direction toward the front of the burner 516 by the sections 558 and 56%. With the necked" construction acting to conduct the heat away from the throat area in both the upstream and downstream directions, heating of the throat area is entirely obviated with the resultant savings of maintenance and operational costs.

While several embodiments described herein are at present considered to be preferred, it is understood that various modifications and improvements may be made therein, and it is intended to cover in the appended claims all such modifications and improvements as fall Within the true spirit and scope of the invention.

What is desired tobe claimed and secured by Letters Patent of the United States is:

1. A high turn-down gas burner adapted to be disposed in and to heat an air stream, comprising burner body means, burner fuel ports defined in said burner body means, generally diverging mixing plate means supported from said body means in air-tight relationship, said plate eans and body means including connecting portions disposed in air-tight relationship such that no air from the air stream passes between the connecting portions to participate in combustion of said fuel, said mixing plate means extending in a direction downstream of said body to be adapted to intercept said air stream and including means for intimately mixing part of the air stream with the burner fuel issuing from said ports at high and intermediate firing rates, and a downstream oriented converging and diverging construction embodied in one of said l; 1 means adjacent the exit side of said ports to define a protective mixing space for low firing rate combustion and to define an offset structure having flame retention characteristics at firing rates other than low firing rates.

2. A high turn-down gas burner adapted to be disposed in and to heat an air stream, comprising burner body means, burner fuel ports defined in said burner body means, generally diverging mixing plate means supported in air-tight fashion from said body means, said plate means and body means having connecting portions connected together so that no air from the air stream passes between them to participate in combustion of said fuel, said mixing plate means extending in a direction downstream of said body means to define a mixing space and including means for intimately mixing in said space part of the air stream with the burner fuel issuing from said ports, a restricted converging and diverging structure including a restricted area embodied in one of said means and located adjacent to and on the exit side of said ports, said structure being constructed so that it performs both a flame retention and a flame protective function, and is adapted to be continuously cooled by the air stream so that any heat developed in the restricted area is dissipated in both upstream and downstream directions and aperture means embodied in one of said means upstream and downstream of said restricted structure for intimately mixing part of the air stream with the burner fuel issuing from said ports.

3. A high turn-down gas burner adapted to be disposed in and to heat an air stream, comprising burner body means, burner fuel ports defined in said burner body means, generally diverging mixing plate means supported in air-tight relation from said body means, said plate means and body means being connected together so that no air from the air stream passes between them, said mixing plate means including means for intimately mixing part of the air stream with the burner fuel issuing from said ports, said mixing plate means embodying a plurality of apertures through which air jets respectively pass for intimate mixture with the burner fuel at intermediate and high firing rates and a restricted converging and diverging structure embodied in one of said means and being so constructed that its inner surface is adapted to be disposed adjacent to the flame issuing from said ports and its outer surface is adapted to be continuously cooled by the air stream so that any heat developed in structure is conducted in both upstream and downstream directions, the portion of said one means upstream of the restricted structure being provided with apertures through which air jets pass for intimate mixture with said burner fuel at low firing rates.

4. A high turn-down gas burner adapted to be disposed in and to heat an air stream, comprising burner body means, burner fuel ports defined in said burner body means, generally diverging mixing plate means supported from said body means in air-tight relationship thereto, said plate means and body means including connecting portions so related that no air from the air stream passes between said portions to participate in combustion of said fuel, said plate means including means for intimately mixing part of the air stream with the burner fuel issuing from said ports, and a necked construction embodied in one of said means and located adjacent the flame side of said ports, said construction adjacent said ports convergingto define for combustion at low firing rates a converging mixing space that is protected from the negative pressure developed by the air stream passing over said mixing plates and, further, including a diverging portion to define with the converging portion a throat that performs a flame retention function at firing rates other than low firing rates.

5. A high turn-down gas burner adapted to be disposed in and to heat an air stream, comprising burner body means, burner fuel ports defined in said burner body means, and generally forwardly diverging mixing plate means supported in air-tight fashion from said body means in air-tight relationship thereto, said plate means and body means including connecting portions so related that no air from the air stream passes between said portions to participate in combustion of said fuel, said plate means including apertures for intimately mixing part of the air stream with the burner fuel issuing from said ports, the mixing plate means being formed so that there is provided adjacent the flame side of said ports inwardly and forwardly converging protective sections defining a protective mixing space for burner fuel combustion at low firing rates and, further, outwardly and forwardly diverging mixing sections defining a mixing space for burner fuel combustion at firing rates other than low firing rates, the sections coacting to define a necked construction that performs both a flame retention and flame protective function.

6. The burner of claim 1 wherein said converging and diverging construction is formed by angulating the upstream ends of the mixing plates and further, said converging-diverging construction is constructed so that it is adapted to be bathed in and cooled by the air stream.

7. The burner of claim 1 wherein said converging and diverging construction comprises part of said body means located on the flame side of and adjacent to said ports, said construction in the body means including inwardly and forwardly converging protective sections defining a protective mixing space for burner fuel combustion at low firing rates and, further, outwardly and forwardly diverging mixing sections defining a mixing space for burner fuel combustion at firing rates other than low firing rates.

8. The burner of claim 7 wherein at least the converging and diverging construction is constructed so that its outer surfaces are adapted to be bathed in and cooled by the air stream.

9. The burner of claim 7 wherein there is additionally provided in said mixing plates and converging and diverging construction of the body means a plurality of apertures that produce a plurality of air jets in said mixing spaces for effecting complete combustion of the burner fuel at all firing rates.

10. The burner of claim 1 wherein said converging and diverging construction comprises part of said mixing plates located immediately adjacent to the flame side of the ports and includes inwardly and forwardly converging protective sections defining a protective mixing space for burner fuel combustion at low firing rates and, further, outwardly and forwardly diverging mixing sections located immediately forwardly of the protective sections for defining a mixing space for burner fuel combustion at firing rates other than low firing rates, and wherein said mixing plates include mixing sections downstream of said convenging and diverging construction embodying inwardly directed projections that perform flame retention functions at intermediate and high firing rates.

11. The burner of claim 10 wherein said mixing plates are constructed so that converging and diverging construction and the projection are adapted to be bathed in and cooled by the air stream.

12. The burner of claim 10 wherein there is additionally provided in said mixing plates means defining a plurality of apertures that direct a plurality of air jets into said mixing spaces for effecting complete combustion of said burner fuel at all firing rates.

13. The burner of claim 1 wherein said converging and diverging construction comprises part of said mixing plates located immediately adjacent to the flame side of the ports and includes protective sections including outwardly and forwardly diverging portions and inwardly and forwardly adjacent converging portions for defining a protective mixing space for burner fuel combustion at low firing rates and, further, outwardly and forwardly diverging mixing sections located immediately forwardly of the protective sections for defining a mixing space for burner fuel combustion at firing rates other than low firing rates.

14. Air stream heating apparatus means for forming an air stream at a velocity of the order of 1500 to 4000 feet per minute, burner body means, burner fuel ports defined in said burner body means, generally diverging mixing plate means supported from said body means in airtight relationship, said plate means and body means having connecting portions in air-tight relation so that no air from the air stream passes between said connecting portions to participate in combustion of said fuel, said plate means including means for intimately mixing part of the air stream with the burner fuel issuing from said port means, and a continuously converging and diverging necked construction embodied in one of said means downstream of said fuel ports for performing a flame protec- References Cited by the Examiner UNITED STATES PATENTS 2,447,482 8/48 Arnold 158-4 2,595,999 5/52 Way et al 158-4 X 3,044,754 7/62 Skerkoske et al 26319 3,051,464 8/62 Yeo et al 263-19 CHARLES SUKALO, Primary Examiner.

JOHN J. CAMBY, Examiner. 

1. A HIGH TURN-DOWN GAS BURNER ADAPTED TO BE DISPOSED IN AND TO HEAT AN AIR STREAM, COMPRISING BURNER BODY MEANS, BURNER FUEL PORTS DEFINED IN SAID BURNER BODY MEANS, GENERALLY DIVERGING MIXING PLATE MEANS SUPPORTED FROM SAID BODY MEANS IN AIR-TIGHT RELATIONSHIP, SAID PLATE MEANS AND BODY MEANS INCLUDING CONNECTING PORTIONS DISPOSED IN AIR-TIGHT RELATIONSHIP SUCH THAT NO AIR FROM THE AIR STREAM PASSES BETWEEN THE CONNECTING PORTIONS TO PARTICIPATE IN COMBUSTION OF SAID FUEL, SAID MIXING PLATE MEANS EXTENDING IN A DIRECTION DOWNSTREAM OF SAID BODY TO BE ADAPTED TO INTERCEPT SAID AIR STREAM AND INCLUDING MEANS FOR INTIMATELY MIXING PART OF THE AIR STREAM WITH THE BURNER FUEL ISSUING FROM SAID PORTS AT HIGH AND INTERMEDIATE FIRING RATES, AND A DOWNSTREAM ORIENTED CONVERGING AND DIVERGING CONSTRUCTION EMBODIED IN ONE OF SAID MEANS ADJACENT THE EXIT SIDE OF SAID PORTS TO DEFINE A PROTECTIVE MIXING SPACE FOR LOW FIRING RATE COMBUSTION AND TO DEFINE AN OFFSET STRUCTURE HAVING FLAME RETENTION CHARACTERISTICS AT FIRING RATES OTHER THAN LOW FIRING RATES. 